全文获取类型
收费全文 | 47588篇 |
免费 | 3647篇 |
国内免费 | 3051篇 |
专业分类
化学 | 13873篇 |
晶体学 | 450篇 |
力学 | 3631篇 |
综合类 | 231篇 |
数学 | 18322篇 |
物理学 | 17779篇 |
出版年
2023年 | 596篇 |
2022年 | 651篇 |
2021年 | 605篇 |
2020年 | 802篇 |
2019年 | 1162篇 |
2018年 | 935篇 |
2017年 | 1015篇 |
2016年 | 969篇 |
2015年 | 779篇 |
2014年 | 1291篇 |
2013年 | 2635篇 |
2012年 | 1697篇 |
2011年 | 2447篇 |
2010年 | 1771篇 |
2009年 | 2392篇 |
2008年 | 2629篇 |
2007年 | 2601篇 |
2006年 | 2449篇 |
2005年 | 1995篇 |
2004年 | 2183篇 |
2003年 | 2262篇 |
2002年 | 2651篇 |
2001年 | 2565篇 |
2000年 | 2356篇 |
1999年 | 2427篇 |
1998年 | 2140篇 |
1997年 | 1458篇 |
1996年 | 860篇 |
1995年 | 614篇 |
1994年 | 511篇 |
1993年 | 366篇 |
1992年 | 330篇 |
1991年 | 317篇 |
1990年 | 357篇 |
1989年 | 312篇 |
1988年 | 264篇 |
1987年 | 207篇 |
1986年 | 203篇 |
1985年 | 282篇 |
1984年 | 272篇 |
1983年 | 113篇 |
1982年 | 212篇 |
1981年 | 302篇 |
1980年 | 285篇 |
1979年 | 153篇 |
1978年 | 205篇 |
1977年 | 148篇 |
1976年 | 101篇 |
1975年 | 95篇 |
1974年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
《Wave Motion》2018
The evolution of surface gravity waves is driven by nonlinear interactions that trigger an energy cascade similarly to the one observed in hydrodynamic turbulence. This process, known as wave turbulence, has been found to display anomalous scaling with deviation from classical turbulent predictions due to the emergence of coherent and intermittent structures on the water surface. In the ocean, waves are spread over a wide range of directions, with a consequent attenuation of the nonlinear properties. A laboratory experiment in a large wave facility is presented to discuss the sensitivity of wave turbulence on the directional properties of model wave spectra. Results show that the occurrence of coherent and intermittent structures become less likely with the broadening of the wave directional spreading. There is no evidence, however, that intermittency completely vanishes. 相似文献
3.
Vyacheslav V. Sentyurin Oleg A. Levitskiy Tatiana V. Magdesieva 《Current Opinion in Electrochemistry》2020
This mini-review highlights key structural features that should be taken into account when creating ambipolar redox-active closed-shell metal-free molecules. This type of compound is strongly required for the fabrication of all-organic ‘poleless’ batteries and semiconductors. The suggested strategies aimed at stabilization of both oxidized (cationic) and reduced (anionic) redox-states are based on the comprehensive analysis of the most successful structures taken from the recent publications. 相似文献
4.
A nanomaterials-based novel molecular beacon has attracted growing attentions in fluorescent assays as many nanomaterials possess excellent quenching efficiency. In this work, a gold-based nanobeacon probe was established to detect organophosphorus pesticides for the first time. The constructed gold-based nanobeacon acted as a signal indicator and could display the decreasing of the intensity in the presence of targets, which competitively bound to single strand DNA. To achieve a high sensitive probe, some parameters including solution pH, temperature and reaction time were investigated and optimized. The gold-based nanobeacon probe assay was proved to be rapid and sensitive to achieve a detection limit of 0.035 μM for isocarbophos, 0.134 μM for profenofos, 0.384 μM for phorate and 2.35 μM for omethoate, respectively. The prepared nanobeacon effectively reduced the background and improved the detection sensitivity and selectivity. The probe is stable, easy to operate and does not need sophisticated instruments. These features makes the probe feasible for screening trace organophosphorus pesticides in real samples. 相似文献
5.
《Arabian Journal of Chemistry》2021,14(11):103421
Processing of Carapa guianensis seeds to obtain oil on an industrial scale generates a significant amount of by-product, approximately 66% w/w, which is called cake and is a potential source of biomolecules, including simple phenolic structures. For this reason, studies were carried out on the chemical profiles of hydrolyzed extract from this agro-industrial by-product through High Performance Thin-Layer Chromatography (HPTLC) and Gas Chromatography coupled to Mass Spectrometry (GC–MS). These techniques were used to detect metabolic classes and/or groups, and to identify, for the first time, thirteen simple phenolic acids in this by-product. The sample antioxidant capacity was determined by methods of 2,2-diphenyl-1-picrylhydrazyl (DPPH)and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS+) radicals direct sequestration. The hydrolyzed fraction showed a total of 63.47% in the relative abundance of the total of compounds, standing out: p-hydroxybenzoic acid (39.19%) and protocatechuic acid (3,4-dihydroxybenzoic acid) (5.62%), both from hydroxybenzoic acids and 3-(3,4-dihydroxyphenyl)lactic acid, (7.76%) hydroxycinnamic acids derivatives. In these results, the fraction rich in simple phenolic acids was obtained, attributing the prominent behavior of this matrix antioxidant activity, expressed by (IC50: of 16.42 µg/mL and 6.52 µg/mL for DPPH and ABTS+ radicals, respectively). The research demonstrated an alternative to applicability that involves sustainability from agro-industrial. These techniques were used to detect metabolic classes and/or groups, and to identify, for the first time, thirteen simple phenolic acids in this by-product, generating a process capable of converting biomass into a bioproduct, consisting of bioactive compounds, in addition to adding value to the industrial chain. 相似文献
6.
Jing Yu Jingwei Han Chuanzhong Li 《Mathematical Methods in the Applied Sciences》2020,43(6):3076-3085
For the orthosymplectic Lie superalgebra , we choose a set of basis matrices. A linear combination of those basis matrices presents a spatial spectral matrix. The compatible condition of the spatial part and the corresponding temporal parts of the spectral problem leads to a generalized super AKNS (GSAKNS) hierarchy. By making use of the supertrace identity, the obtained GSAKNS hierarchy can be written as the super bi-Hamiltonian structures. 相似文献
7.
8.
The behaviors of ferromagnetic transition metals of the first period: Fe, Co and Ni are examined within density functional theory calculations in two dimensional carbon extended networks using model structure LiC6. Around geometry optimized structures, the energy-volume equations of states considering non magnetic and spin polarized configurations established ferromagnetic ground states with magnetizations –reduced with respect to the metals’– of 2 μB for FeC6 and 1 μB for CoC6 while no magnetic solution could be identified for NiC6. In the D6h point group of the P6/mmm space group lm decomposition of the d states results with increasing energy into doublet state E1g with d(x2-y2) and d(xy); singlet state A1g d(z2) and doublet state E2g d(xz) and d(yz) lying on EF and responsible of the onset of magnetic moments. This was mirrored via molecular orbital approach with a construct of Fe embedded between two extended carbon networks thus validating the model structure proposed for TC6 compounds. The 100% polarization in one spin channel allows proposing potential uses in spintronics applications. 相似文献
9.
This work is concerned with the extension of the Jacobi spectral Galerkin method to a class of nonlinear fractional pantograph differential equations. First, the fractional differential equation is converted to a nonlinear Volterra integral equation with weakly singular kernel. Second, we analyze the existence and uniqueness of solutions for the obtained integral equation. Then, the Galerkin method is used for solving the equivalent integral equation. The error estimates for the proposed method are also investigated. Finally, illustrative examples are presented to confirm our theoretical analysis. 相似文献
10.